Non-secular simulation of frequency domain two-pulse powder ESEEM signals in multinuclear systems Original Research Article

We have developed a general non-perturbative theory, which simulates the two-pulse ESEEM signals of disordered solids directly by using the eigenvalues and eigenvectors of the non-secular Liouville superoperator. The present theory can handle multinuclear systems of arbitrary nuclear spin quantum number (up to 92), systems with rhombic g, hfi (hyperfine interaction) and nqi (nuclear quadrupole interaction) tensor with arbitrary relative orientations and strengths. The simulations presented here are for the two-pulse (primary) ESEEM signals under total excitation conditions. Non-secular powder simulations at the L-band, and at lower fields, for large g-tensor anisotropy and/or intermediate hfi differ appreciably from their secular counterparts. Since the high-field approximation for the electron spin is not required in the present theory we can even simulate the echo modulation for strongly coupled, isotropic electron-nuclear systems, and the echo modulation for systems with anisotropy only in the g-tensor.